Method and apparatus for video coding without updating the HMVP table

ABSTRACT

A method for video decoding at a video decoder is described. A merge sharing region including a plurality of coding blocks can be received. A shared merge candidate list is constructed for the merge sharing region. The merge sharing region is decoded based on the shared merge candidate list. At least one inter coded coding block within the merge sharing region is processed without updating a history-based motion vector prediction (HMVP) table with motion information of the at least one inter coded coding block.

INCORPORATION BY REFERENCE

This present application claims the benefit of priority to U.S.Provisional Application No. 62/793,872, “Method of HMVP Buffer UpdateWhen Shared Merge List Is Used” filed on Jan. 17, 2019, which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 ((102) through (106), respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide a method for video decoding at a videodecoder. A merge sharing region including a plurality of coding blockscan be received. A shared merge candidate list is constructed for themerge sharing region. The merge sharing region is decoded based on theshared merge candidate list. At least one inter coded coding blockwithin the merge sharing region is processed without updating ahistory-based motion vector prediction (HMVP) table with motioninformation of the at least one inter coded coding block.

In an example, all inter coded blocks in the merge sharing region areprocessed without updating the HMVP table with motion information of anyof the inter coded blocks. In an example, the coding block(s) within themerge sharing region that is inter coded with a merge mode or a skipmode is processed without updating the HMVP table with motioninformation of the coding block(s). In an example, the coding block(s)within the merge sharing region that is inter coded (i) using a mergecandidate on the shared merge candidate list as motion information ofthe coding block(s), or (ii) using motion information determined basedon a merge candidate on the shared merge candidate list is processedwithout updating the HMVP table with motion information of the codingblock(s). In an embodiment, the coding block(s) within the merge sharingregion that is coded based on the shared merge candidate list isprocessed without updating the HMVP table with motion information of thecoding block(s).

In an example, the coding block(s) within the merge sharing region thatis inter coded using a merge candidate on the shared merge candidatelist as motion information of the coding block(s) is processed withoutupdating the HMVP table with motion information of the coding block(s).

In an example, motion information of the first inter coded coding blockwithin the merge sharing region according to a decoding order is used toupdate the HMVP table, and the other inter coded coding block(s) withinthe merge sharing region is processed without updating the HMVP tablewith motion information of the other inter coded coding block(s). In anexample, motion information of the last inter coded coding block withinthe merge sharing region according to a decoding order is used to updatethe HMVP buffer, and the other inter coded coding block(s) within themerge sharing region is processed without updating the HMVP buffer withmotion information of the other inter coded coding block(s).

Aspects of the disclosure provide an apparatus of video decoding. Theapparatus can include circuitry configured to receive a merge sharingregion including a plurality of coding blocks. The circuitry can furtherbe configured to construct a shared merge candidate list for the mergesharing region, and decode the merge sharing region based on the sharedmerge candidate list. At least one inter coded coding block within themerge sharing region is processed without updating an HMVP table withmotion information of the at least one inter coded coding block.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 is a schematic illustration of merge candidate positions of amerge mode in accordance with an embodiment.

FIG. 9 is a schematic illustration of spatial neighboring blocks andtemporal neighboring blocks for a current block in accordance with anembodiment.

FIG. 10A is a schematic illustration of spatial neighboring blocks thatcan be used to determine predicting motion information for a currentblock using a sub-block based temporal motion vector prediction methodbased on motion information of the spatial neighboring blocks inaccordance with one embodiment.

FIG. 10B is a schematic illustration of a selected spatial neighboringblock for a sub-block based temporal motion vector prediction method inaccordance with one embodiment.

FIG. 11A is a flow chart outlining a process of constructing andupdating a list of motion information candidates using a history basedmotion vector prediction method in accordance with one embodiment.

FIG. 11B is a schematic illustration of updating the list of motioninformation candidates using the history based motion vector predictionmethod in accordance with one embodiment.

FIG. 12 is a schematic illustration of determining starting points attwo reference pictures associated with two reference picture lists basedon motion vectors of a merge candidate in a merge with motion vectordifference (MMVD) mode in accordance with an embodiment.

FIG. 13 is a schematic illustration of predetermined points surroundingtwo starting points that are to be evaluated in the MMVD mode inaccordance with an embodiment.

FIGS. 14A-14B show examples of merge sharing regions in accordance withan embodiment.

FIG. 15 shows a table of inter prediction modes that can be used forencoding or decoding sub-blocks within a merge sharing region inaccordance with some embodiments.

FIG. 16 is a flow chart outlining a video decoding process for decodinga merge sharing region in accordance with an embodiment.

FIG. 17 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

I. Video Coding Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

II. Inter Picture Prediction Modes

In various embodiments, a picture can be partitioned into blocks, forexample, using a tree structure based partition scheme. The resultingblocks can then be processed with different processing modes, such as anultra prediction mode, an inter prediction mode (e.g., merge mode, skipmode, advanced motion vector prediction (AVMP) mode), and the like. Anintra coded block can be a block that is coded with an intra predictionmode. In contrast, an inter coded block can be a bock that is processedwith an inter prediction mode.

Examples of inter prediction modes can be classified into twocategories: (i) AMVP mode, and (ii) merge/skip mode. Examples of themerge/skip mode can include HEVC merge mode (or regular merge mode),current reference picture (CRP) mode (or intra block copy (IBC)) mode,triangle partition mode, subblock-based temporal motion vectorprediction (sbTMVP) mode, merge with motion vector difference (MMVD)mode, and affine merge mode. In some embodiments, the AMVP mode and themerge/skip mode can be combined with a history-based motion vectorprediction (HMVP) table to encoding or decoding a coding block.

Examples of inter prediction modes and employment of HMVP tables aredescribed below.

1. Regular Merge Mode

When a currently processed block, referred to as a current block, isprocessed with a merge mode, a neighboring block can be selected from aspatial or temporal neighborhood of the current block. The current blockcan be merged with the selected neighboring block by sharing a same setof motion data (or referred to as motion information) from the selectedneighboring block. This merge mode operation can be performed over agroup of neighboring blocks, such that a region of neighboring blockscan be merged together and share a same set of motion data. Duringtransmission from an encoder to a decoder, an index indicating themotion data of the selected neighboring block can be transmitted for thecurrent block, instead of transmission of the whole set of motion data.In this way, an amount of data (bits) that are used for transmission ofmotion information can be reduced, and coding efficiency can beimproved.

In the above example, the neighboring block, which provides the motiondata, can be selected from a set of candidate positions. The candidatepositions can be predefined with respect to the current block. Forexample, the candidate positions can include spatial candidate positionsand temporal candidate positions. Each spatial candidate position isassociated with a spatial neighboring block neighboring the currentblock. Each temporal candidate position is associated with a temporalneighboring block located in another coded picture (e.g., a previouslycoded picture). Neighboring blocks overlapping the candidate positions(referred to as candidate blocks) are a subset of all the spatial ortemporal neighboring blocks of the current block. In this way, thecandidate blocks can be evaluated for selection of a to-be-merged blockinstead of the whole set of neighboring blocks.

FIG. 8 shows an example of candidate positions. From those candidatepositions, a set of merge candidates can be selected to construct amerge candidate list. As shown, a current block (810) is to be processedwith merge mode. A set of candidate positions {A1, B1, B0, A0, B2, C0,C1} are defined for the merge mode processing. Specifically, candidatepositions {A1, B1, B0, A0, B2} are spatial candidate positions thatrepresent positions of candidate blocks that are in the same picture asthe current block (810). In contrast, candidate positions {C0, C1} aretemporal candidate positions that represent positions of candidateblocks that are in another coded picture and neighbor or overlap aco-located block of the current block (810). As shown, the candidateposition C1 can be located near (e.g., adjacent to) a center of thecurrent block (810).

A candidate position can be represented by a block of samples or asample in different examples. In FIG. 8, each candidate position isrepresented by a block of samples, for example, having a size of 4×4samples. A size of such a block of samples corresponding to a candidateposition can be equal to or smaller than a minimum allowable size of PBs(e.g., 4×4 samples) defined for a tree-based partitioning scheme usedfor generating the current block (810). Under such a configuration, ablock corresponding to a candidate position can always be covered withina single neighboring PB. In an alternative example, a sample position(e.g., a bottom-right sample within the block A1, or a top-right samplewithin the block A0) may be used to represent a candidate position. Sucha sample is referred to as a representative sample, while such aposition is referred to as a representative position.

In one example, based on the candidate positions {A1, B1, B0, A0, B2,C0, C1} defined in FIG. 8, a merge mode process can be performed toselect merge candidates from the candidate positions {A1, B1, B0, A0,B2, C0, C1} to construct a candidate list. The candidate list can have apredefined maximum number of merge candidates, represented as Cm. Eachmerge candidate in the candidate list can include a set of motion datathat can be used for motion-compensated prediction.

The merge candidates can be listed in the candidate list according to acertain order. For example, depending on how the merge candidate isderived, different merge candidates may have different probabilities ofbeing selected. The merge candidates having higher probabilities ofbeing selected are positioned in front of the merge candidates havinglower probabilities of being selected. Based on such an order, eachmerge candidate is associated with an index (referred to as a mergeindex). In one embodiment, a merge candidate having a higher probabilityof being selected will have a smaller index value such that fewer bitsare needed for coding the respective index.

In one example, the motion data of a merge candidate can includehorizontal and vertical motion vector displacement values of one or twomotion vectors, one or two reference picture indices associated with theone or two motion vectors, and optionally an identification of whichreference picture list is associated with an reference picture index.

In an example, according to a predefined order, a first number of mergecandidates, Ca, is derived from the spatial candidate positionsaccording to the order {A1, B1, B0, A0, B2}, and a second number ofmerge candidates, Cb=Cm−Ca, is derived from the temporal candidatepositions according to the order {C0, C1}. The numerals A1, B1, B0, A0,B2, C0, C1 for representing candidate positions can also be used torefer to merge candidates. For example, a merge candidate obtained fromcandidate position A1 is referred to as the merge candidate A1.

In some scenarios, a merge candidate at a candidate position may beunavailable. For example, a candidate block at a candidate position canbe intra-predicted, outside of a slice or tile including the currentblock (810), or not in a same coding tree block (CTB) row as the currentblock (810). In some scenarios, a merge candidate at a candidateposition may be redundant. For example, one neighboring block of thecurrent block (810) can overlap two candidate positions. The redundantmerge candidate can be removed from the candidate list (e.g., byperforming a pruning process). When a total number of available mergecandidates (with redundant candidates being removed) in the candidatelist is smaller than the maximum number of merge candidates Cm,additional merge candidates can be generated (e.g., according to apreconfigured rule) to fill the candidate list such that the candidatelist can be maintained to have a fixed length. For example, additionalmerge candidates can include combined bi-predictive candidates and zeromotion vector candidates.

After the candidate list is constructed, at an encoder, an evaluationprocess can be performed to select a merge candidate from the candidatelist. For example, rate-distortion (RD) performance corresponding toeach merge candidate can be calculated, and the one with the best RDperformance can be selected. Accordingly, a merge index associated withthe selected merge candidate can be determined for the current block(810) and signaled to a decoder.

At a decoder, the merge index of the current block (810) can bereceived. A similar candidate list construction process, as describedabove, can be performed to generate a candidate list that is the same asthe candidate list generated at the encoder side. After the candidatelist is constructed, a merge candidate can be selected from thecandidate list based on the received merge index without performing anyfurther evaluations in some examples. Motion data of the selected mergecandidate can be used for a subsequent motion-compensated prediction ofthe current block (810).

A skip mode is also introduced in some examples. For example, in theskip mode, a current block can be predicted using a merge mode asdescribed above to determine a set of motion data, however, no residueis generated, and no transform coefficients are transmitted. A skip flagcan be associated with the current block. The skip flag and a mergeindex indicating the related motion information of the current block canbe signaled to a video decoder. For example, at the beginning of a CU inan inter-picture prediction slice, a skip flag can be signaled thatimplies the following: the CU only contains one PU (2N×2N); the mergemode is used to derive the motion data; and no residual data is presentin the bitstream. At the decoder side, based on the skip flag, aprediction block can be determined based on the merge index for decodinga respective current block without adding residue information. Thus,various methods for video coding with merge mode disclosed herein can beutilized in combination with a skip mode.

As an example, in an embodiment, when a merge flag or a skip flag issignaled as true in a bitstream, a merge index is then signaled toindicate which candidate in a merge candidate list will be used toprovide motion vectors for a current block. Up to four spatiallyneighboring motion vectors and up to one temporally neighboring motionvectors can be added to the merge candidate list. A syntaxMaxMergeCandsNum is defined as the size of the merge candidate list. Thesyntax MaxMergeVandsNum can be signaled in the bitstream.

2. Affine Merge Mode

FIG. 9 is a schematic illustration of spatial neighboring blocks and atemporal neighboring block of a current block (or referred to as acoding unit (CU)) (901) in accordance with an embodiment. As shown, thespatial neighboring blocks are denoted A0, A1, A2, B0, B1, B2, and B3(902, 903, 907, 904, 905, 906, and 908, respectively), and the temporalneighboring block are denoted C0 (912). In some examples, the spatialneighboring blocks A0, A1, A2, B0, B1, B2, and B3 and the current block(901) belong to a same picture. In some examples, the temporalneighboring block C0 belongs to a reference picture and corresponds to aposition outside the current block (901) and adjacent to a lower-rightcorner of the current block (901).

In some examples, a motion vector of the current block (901) and/orsub-blocks of the current block can be derived using an affine model(e.g., a 6-parameter affine model or a 4-parameter affine model). Insome examples, an affine model has 6 parameters (e.g., a 6-parameteraffine model) to describe the motion vector of a block. In an example,the 6 parameters of an affine coded block can be represented by threemotion vectors (also referred to as three control point motionvectors(CPMVs)) at three different locations of the block (e.g., controlpoints CP0, CP1, and CP2 at upper-left, upper-right, and lower-leftcorners in FIG. 9). In another example, a simplified affine model usesfour parameters to describe the motion information of an affine codedblock, which can be represented by two motion vectors (also referred toas two CPMVs) at two different locations of the block (e.g., controlpoints CP0 and CP1 at upper-left and upper-right corners in FIG. 9).

A list of motion information candidates (also referred to as an affinemerge candidate list) can be constructed using an affine merge modebased on motion information of one or more of the spatial neighboringblocks and/or temporal neighboring blocks. In some examples, the affinemerge mode can be applied when the current block (901) has a width andheight that are equal to or greater than 8 samples. According to theaffine merge mode, the CPMVs of the current block (901) can bedetermined based on the motion information candidates on the list. Insome examples, the list of motion information candidates can include upto five CPMV candidates, and an index can be signaled to indicate whichCPMV candidate is to be used for the current block.

In some embodiments, the affine merge candidate list can have threetypes of CPVM candidates, including inherited affine candidates,constructed affine candidates, and a zero MV. An inherited affinecandidate can be derived by extrapolation from the CPMVs of theneighboring blocks. A constructed affine candidate can be derived usingthe translational MVs of the neighboring blocks.

In an example, there can be at most two inherited affine candidates,which are derived from corresponding affine motion models of theneighboring blocks, including one block from left neighboring blocks (A0and A1) and one from upper neighboring blocks (B0, B1, and B2). For thecandidate from the left, neighboring blocks A0 and A1 can besequentially checked, and a first available inherited affine candidatefrom neighboring blocks A0 and A1 is used as the inherited affinecandidate from the left. For the candidate from the top, neighboringblocks B0, B1, and B2 can be sequentially checked, and a first availableinherited affine candidate from neighboring blocks B0, B1, and B2 isused as the inherited affine candidate from the top. In some examples,no pruning check is performed between the two inherited affinecandidates.

When a neighboring affine block is identified, a corresponding inheritedaffine candidate to be added to the affine merge list of the currentblock (901) can be derived from the control point motion vectors of theneighboring affine block. In the FIG. 9 example, if the neighboringblock A1 is coded in affine mode, the motion vectors of the upper-leftcorner (control point CP0 _(A1)), the upper-right corner (control pointCP1 _(A1)), and the lower-left corner (control point CP2 _(A1)) of blockA1 can be obtained. When block A1 is coded using a 4-parameter affinemodel, the two CPMVs as an inherited affine candidate of the currentblock (901) can be calculated according to the motion vectors of controlpoint CP0 _(A1) and control point CP1 _(A1). When block A1 is codedusing a 6-parameter affine model, the three CPMVs as an inherited affinecandidate of the current block (901) can be calculated according to themotion vectors of control point CP0 _(A1), control point CP1 _(A1), andcontrol point CP2 _(A1).

Moreover, a constructed affine candidate can be derived by combining theneighboring translational motion information of each control point. Themotion information for the control points CP0, CP1, and CP2 is derivedfrom the specified spatial neighboring blocks A0, A1, A2, B0, B1, B2,and B3.

For example, CPMV_(k) (k=1, 2, 3, 4) represents the motion vector of thek-th control point, where CPMV₁ corresponds to control point CP0, CPMV₂corresponds to control point CP1, CPMV₃ corresponds to control pointCP2, and CPMV₄ corresponds to a temporal control point based on temporalneighboring block C0. For CPMV₁, neighboring blocks B2, B3, and A2 canbe sequentially checked, and a first available motion vector fromneighboring blocks B2, B3, and A2 is used as CPMV₁. For CPMV₂,neighboring blocks B1 and B0 can be sequentially checked, and a firstavailable motion vector from neighboring blocks B1 and B0 is used asCPMV₂. For CPMV₃, neighboring blocks A1 and A0 can be sequentiallychecked, and a first available motion vector from neighboring blocks A1and A0 is used as CPMV₃. Moreover, the motion vector of temporalneighboring block C0 can be used as CPMV₄, if available.

After CPMV₁, CPMV₂, CPMV₃, and CPMV₄, of four control points CP0, CP1,CP2 and the temporal control point are obtained, an affine mergecandidate list can be constructed to include affine merge candidatesthat are constructed in an order of: {CPMV₁, CPMV₂, CPMV₃}, {CPMV₁,CPMV₂, CPMV₄}, {CPMV₁, CPMV₃, CPMV₄}, {CPMV₂, CPMV₃, CPMV₄}, {CPMV₁,CPMV₂}, and {CPMV₁, CPMV₃}. Any combination of three CPMVs can form a6-parameter affine merge candidate, and any combination of two CPMVs canform a 4-parameter affine merge candidate. In some examples, in order toavoid a motion scaling process, if the reference indices of a group ofcontrol points are different, the corresponding combination of CPMVs canbe discarded.

3. Subblock-Based Temporal Motion Vector Prediction (SbTMVP) Mode

FIG. 10A is a schematic illustration of spatial neighboring blocks thatcan be used to determine predicting motion information for a currentblock (1011) using a sub-block based temporal MV prediction (SbTMVP)method based on motion information of the spatial neighboring blocks inaccordance with one embodiment. FIG. 10A shows a current block (1011)and its spatial neighboring blocks denoted A0, A1, B0, and B1 (1012,1013, 1014, and 1015, respectively). In some examples, spatialneighboring blocks A0, A1, B0, and B1 and the current block (1011)belong to a same picture.

FIG. 10B is a schematic illustration of determining motion informationfor sub-blocks of the current block (1011) using the SbTMVP method basedon a selected spatial neighboring block, such as block A1 in thisnon-limiting example, in accordance with an embodiment. In this example,the current block (1011) is in a current picture (1010), and a referenceblock (1061) is in a reference picture (1060) and can be identifiedbased on a motion shift (or displacement) between the current block(1011) and the reference block (1061) indicated by a motion vector(1022).

In some embodiments, similar to a temporal motion vector prediction(TMVP) in HEVC, a SbTMVP uses the motion information in variousreference sub-blocks in a reference picture for a current block in acurrent picture. In some embodiments, the same reference picture used byTMVP can be used for SbTVMP. In some embodiments, TMVP predicts motioninformation at a CU level but SbTMVP predicts motion at a sub-CU level.In some embodiments, TMVP uses the temporal motion vectors fromcollocated block in the reference picture, which has a correspondingposition adjacent to a lower-right corner or a center of a currentblock, and SbTMVP uses the temporal motion vectors from a referenceblock, which can be identified by performing a motion shift based on amotion vector from one of the spatial neighboring blocks of the currentblock.

For example, as shown in FIG. 10A, neighboring blocks A1, B1, B0, and A0can be sequentially checked in a SbTVMP process. As soon as a firstspatial neighboring block that has a motion vector that uses thereference picture (1060) as its reference picture is identified, such asblock A1 having the motion vector (1022) that points to a referenceblock AR1 in the reference picture (1060) for example, this motionvector (1022) can be used for performing the motion shift. If no suchmotion vector is available from the spatial neighboring blocks A1, B1,B0, and A0, the motion shift is set to (0, 0).

After determining the motion shift, the reference block (1061) can beidentified based on a position of the current block (1011) and thedetermined motion shift. In FIG. 10B, the reference block (1061) can befurther divided into 16 sub-blocks with reference motion information MRathrough MRp. In some examples, the reference motion information for eachsub-block in the reference block (1061) can be determined based on asmallest motion grid that covers a center sample of such sub-block. Themotion information can include motion vectors and correspondingreference indices. The current block (1011) can be further divided into16 sub-blocks, and the motion information MVa through MVp for thesub-blocks in the current block (1011) can be derived from the referencemotion information MRa through MRp in a manner similar to the TMVPprocess, with temporal scaling in some examples.

The sub-block size used in the SbTMVP process can be fixed (or otherwisepredetermined) or signaled. In some examples, the sub-block size used inthe SbTMVP process can be 8×8 samples. In some examples, the SbTMVPprocess is only applicable to a block with a width and height equal toor greater than the fixed or signaled size, for example 8 pixels.

In an example, a combined sub-block based merge list which contains aSbTVMP candidate and affine merge candidates is used for the signalingof a sub-block based merge mode. The SbTVMP mode can be enabled ordisabled by a sequence parameter set (SPS) flag. In some examples, ifthe SbTMVP mode is enabled, the SbTMVP candidate is added as the firstentry of the list of sub-block based merge candidates, and followed bythe affine merge candidates. In some embodiments, the maximum allowedsize of the sub-block based merge list is set to five. However, othersizes may be utilized in other embodiments.

In some embodiments, the encoding logic of the additional SbTMVP mergecandidate is the same as for the other merge candidates. That is, foreach block in a P or B slice, an additional rate-distortion check can beperformed to determine whether to use the SbTMVP candidate.

4. History-Based Motion Vector Prediction (HMVP) Mode

FIG. 11A is a flow chart outlining a process (1100) of constructing andupdating a list of motion information candidates using a history basedMV prediction (HMVP) method in accordance with one embodiment.

In some embodiments, a list of motion information candidates using theHMVP method can be constructed and updated during an encoding ordecoding process. The list can be referred to as a history list. Thehistory list can be stored in forms of an HMVP table or an HMVP buffer.The history list can be emptied when a new slice begins. In someembodiments, whenever there is an inter-coded non-affine block that isjust encoded or decoded, the associated motion information can be addedto a last entry of the history list as a new HMVP candidate. Therefore,before processing (encoding or decoding) a current block, the historylist with HMVP candidates can be loaded (S1112). The current block canbe encoded or decoded using the HMVP candidates in the history list(S1114). Afterwards, the history list can be updated using the motioninformation for encoding or decoding the current block (S1116).

FIG. 11B is a schematic illustration of updating the list of motioninformation candidates using the history based MV prediction method inaccordance with one embodiment. FIG. 11B shows a history list having asize of L, where each candidate in the list can be identified with anindex ranging from 0 to L−1. L is an integer equal to or greater than 0.Before encoding or decoding a current block, the history list (1120)includes L candidates HMVP₀, HMVP₁, HMVP₂, . . . HMVP_(m), . . . ,HMVP_(L-2), and HMVP_(L-1), where m is an integer ranging from 0 to L.After encoding or decoding a current block, a new entry HMVP_(C) is tobe added to the history list.

In an example, the size of the history list can be set to 6, whichindicates up to 6 HMVP candidates can be added to the history list. Wheninserting a new motion candidate (e.g., HMVP_(C)) to the history list, aconstrained first-in-first-out (FIFO) rule can be utilized, wherein aredundancy check is first applied to find whether there is a redundantHMVP in the history list. When no redundant HMVP is found, the firstHMVP candidate (HMVP₁ in FIG. 11B example, with index=0) is removed fromthe list, and all other HMVP candidates afterwards are moved forward,e.g., with indices reduced by 1. The new HMVP_(C) candidate can be addedto the last entry of the list (with index=L−1 in FIG. 11B for example),as shown in the resulting list (1130). On the other hand, if a redundantHMVP is found (such as HMVP₂ in FIG. 11B example), the redundant HMVP inthe history list is removed from the list, and all the HMVP candidatesafterwards are moved forward, e.g., with indices reduced by 1. The newHMVP_(C) candidate can be added to the last entry of the list (withindex=L−1 in FIG. 11B for example), as shown in the resulting list(1140).

In some examples, the HMVP candidates could be used in the mergecandidate list construction process. For example, the latest HMVPcandidates in the list can be checked in order and inserted into thecandidate list after a TMVP candidate. Pruning can be applied on theHMVP candidates against the spatial or temporal merge candidates, butnot the sub-block motion candidates (i.e., SbTMVP candidates) in someembodiments.

In some embodiments, to reduce the number of pruning operations, one ormore of the following rules can be followed:

-   -   (a) Number of HMPV candidates to be checked denoted by M is set        as follows:        M=(N<=4)?L:(8−N),    -   wherein N indicates a number of available non-sub block merge        candidates, and L indicates number of available HMVP candidates        in the history list.    -   (b) In addition, once the total number of available merge        candidates becomes only one less than a signaled maximum number        of merge candidates, the merge candidate list construction        process from HMVP list can be terminated.    -   (c) Moreover, the number of pairs for combined bi-predictive        merge candidate derivation can be reduced from 12 to 6.

In some embodiments, HMVP candidates can be used in an AMVP candidatelist construction process. The motion vectors of the last K HMVPcandidates in the history list can be added to an AMVP candidate listafter a TMVP candidate. In some examples, only HMVP candidates with thesame reference picture as an AMVP target reference picture are to beadded to the AMVP candidate list. Pruning can be applied on the HMVPcandidates. In some examples, K is set to 4 while the AMVP list size iskept unchanged, e.g., equal to 2.

5. Pairwise Average Motion Vector Candidates

In some embodiments, pairwise average candidates can be generated byaveraging predefined pairs of candidates in a current merge candidatelist. For example, the predefined pairs are defined as {(0, 1), (0, 2),(1, 2), (0, 3), (1, 3), (2, 3)} in an embodiment, where the numbersdenote the merge indices to the merge candidate list. For example, theaveraged motion vectors are calculated separately for each referencepicture list. If both to-be-averaged motion vectors are available in onelist, these two motion vectors are averaged even when they point todifferent reference pictures. If only one motion vector is available,the available one can be used directly. If no motion vector isavailable, the respective pair is skipped in one example. The pairwiseaverage candidates replace the combined candidates in some embodimentsin constructing a merge candidate list.

6. Merge with Motion Vector Difference (MMVD) Mode

In some embodiments, a merge with motion vector difference (MMVD) modeis used for determining a motion vector predictor of a current block.The MMVD mode can be used when skip mode or merge mode is enabled. TheMMVD mode reuses merge candidates on a merge candidate list of the skipmode or merge mode. For example, a merge candidate selected from themerge candidate list can be used to provide a starting point at areference picture. A motion vector of the current block can be expressedwith the starting point and a motion offset including a motion magnitudeand a motion direction with respect to the starting point. At an encoderside, selection of the merge candidate and determination of the motionoffset can be based on a search process (an evaluation process). At adecoder side, the selected merge candidate and the motion offset can bedetermined based on signaling from the encoder side.

The MMVD mode can reuse a merge candidate list constructed in variousinter prediction modes described herein. In some examples, onlycandidates of a default merge type (e.g., MRG_TYPE_DEFAULT_N) on themerge candidate list are considered for MMVD mode. Examples of the mergecandidates of the default merge types can include (i) merge candidatesemployed in the merge mode, (ii) merge candidates from a history bufferin the HMVP mode, and (iii) pairwise average motion vector candidates asdescribed herein. Merge candidates in the affine mode or SbTMVP mode arenot used for expansion in MMVD mode in some examples.

A base candidate index (IDX) can be used to define the starting point.For example, a list of merge candidates (motion vector predicators(MVPs)) associated with indices from 0 to 3 is shown in Table 1. Themerge candidate having an index of the base candidate index can bedetermined from the list, and used to provide the starting point.

TABLE 1 Base candidate IDX Base candidate IDX 0 1 2 3 N^(th) MVP 1^(st)MVP 2^(nd) MVP 3^(rd) MVP 4^(th) MVP

A distance index can be used to provide motion magnitude information.For example, a plurality of predefined pixel distances are shown inTable 2 each associated with indices from 0 to 7. The pixel distancehaving an index of the distance index can be determined from theplurality of pixel distances, and used to provide the motion magnitude.

TABLE 2 Distance IDX Distance IDX 0 1 2 3 4 5 6 7 Pixel ¼-pel ½-pel1-pel 2-pel 4-pel 8-pel 16-pel 32-pel distance

A direction index can be used to provide motion direction information.For example, four directions with indices from 00 to 11 (binary) areshown in Table 3. The direction with an index of the direction index canbe determined from the four directions, and used to provide a directionof the motion offset with respect to the starting point.

TABLE 3 Direction IDX Direction IDX 00 01 10 11 x-axis + − N/A N/Ay-axis N/A N/A + −

MMVD syntax elements can be transmitted in a bitstream to signal a setof MMVD indices including a base candidate index, a direction index, anda distance IDX in the MMVD mode.

In some embodiments, an MMVD enable flag is signaled after sending askip and merge flag for coding a current block. For example, when theskip and merge flag is true, the MMVD flag is parsed. When the MMVD flagis equal to 1, in an example, the MMVD syntax elements (the set of MMVDindices) are parsed. In one example, when the MMVD flag is not 1, a flagassociated with another mode, such as an AFFINE flag, is parsed. Whenthe AFFINE flag is equal to 1, the AFFINE mode is used for processingthe current block. When the AFFINE flag is not 1, in an example, askip/merge index is parsed for processing the current block withskip/merge mode.

FIGS. 12-13 show an example of a search process in MMVD mode accordingto an embodiment of the disclosure. By performing the search process, aset of MMVD indices including a base candidate index, a direction index,and a distance index can be determined for a current block (1201) in acurrent picture (or referred to as a current frame).

As shown in FIGS. 12-13, a first motion vector (1211) and a secondmotion vector (1221) belonging to a first merge candidate are shown. Thefirst merge candidate can be a merge candidate on a merge candidate listconstructed for the current block (1201). The first and second motionvectors (1211) and (1221) can be associated with two reference pictures(1202) and (1203) in reference picture lists L0 and L1, respectively.Accordingly, two starting points (1311) and (1321) in FIG. 13 can bedetermined at the reference pictures (1202) and (1203).

In an example, based on the starting points (1311) and (1321), multiplepredefined points extending from the starting points (1311) and (1321)in vertical directions (represented by +Y, or −Y) or horizontaldirections (represented by +X and −X) in the reference pictures (1202)and (1203) can be evaluated. In one example, a pair of points mirroringeach other with respect to the respective starting point (1311) or(1321), such as the pair of points (1314) and (1324), or the pair ofpoints (1315) and (1325), can be used to determine a pair of motionvectors which may form a motion vector predictor candidate for thecurrent block (1201). Those motion vector predictor candidatesdetermined based on the predefined points surrounding the startingpoints (1311) or (1321) can be evaluated.

In addition to the first merge candidate, other available or valid mergecandidates on the merge candidate list of the current block (1201) canalso be evaluated similarly. In one example, for a uni-predicted mergecandidate, only one prediction direction associated with one of the tworeference picture lists is evaluated.

Based on the evaluations, a best motion vector predictor candidate canbe determined. Accordingly, corresponding to the best motion vectorpredictor candidate, a best merge candidate can be selected from themerge list, and a motion direction and a motion distance can also bedetermined. For example, based on the selected merge candidate and theTable 1, a base candidate index can be determined. Based on the selectedmotion vector predictor, such as that corresponding to the predefinedpoint (1315) (or (1325)), a direction and a distance of the point (1315)with respect to the starting point (1311) can be determined. Accordingto Table 2 and Table 3, a direction index and a distance index canaccordingly be determined.

It is noted that the examples described above are merely forillustrative purpose. In alternative examples, based on the motionvector expression method provided in the MMVD mode, the motion distancesand motion directions may be defined differently. In addition, theevaluation process (search process) may be performed differently. Forexample, for a bi-prediction merge candidate, three types of predictiondirections (e.g., L0, L1, and L0 and L1) may be evaluated based on a setof predefined distances and directions to select a best motion vectorpredictor. For another example, a uni-predicted merge candidate may beconverted by mirroring or scaling to a bi-predicted merge candidate, andsubsequently evaluated. In the above examples, an additional syntaxindicating a prediction direction (e.g., L0, L1, or L0 and L1) resultingfrom the evaluation process may be signaled.

As described above, merge candidates on a merge candidate list areevaluated to determine a base candidate in the MMVD mode at an encoder.At a decoder, using a base candidate index as input, a motion vectorpredictor can be selected from a merge candidate list. Accordingly, noadditional line buffer is needed for the MMVD mode in addition to a linebuffer for storage of the merge candidates.

III. Merge Sharing Region with a Shared Merge List

In some embodiments, a merge sharing region with a shared merge list isemployed when a size of a current block and/or sizes of sub-blockswithin the current block meet certain conditions. For example, leaf CUsof an ancestor node in a CU split tree can share a merge candidate list.In this way, separately construction of a merge candidate list for eachof the leaf CUs can be avoided, which enables parallel processing ofsmall merge/skip-coded CUs within a merge sharing region. The ancestornode is named a merge sharing node or a merge sharing region. The sharedmerge candidate list is generated for the merge sharing node pretendingthe merge sharing node is a leaf CU.

Whether a split-tree node can be treated as a merge sharing node can bedecided for each node inside a CTU during a parsing stage of decoding.In an example, an ancestor node of leaf CUs can be determined to be amerge sharing node when the ancestor node satisfies the followingcriteria:

-   -   (a) The block size of the ancestor node is equal to or larger        than a size threshold (e.g., 32 pixels, 64 pixels, or the like);    -   (b) Within the ancestor node, one of the child CU has a size        smaller than the size threshold.

FIG. 14A shows examples of merge sharing regions (1401)-(1404) definedbased on a size threshold of 64 pixels. Each of the merge sharingregions (1401)-(1404) has a block size of 64 pixels equal to the sizethreshold. Each of the merge sharing regions (1401)-(1404) includes atleast one leaf CU having a size smaller than the size threshold.

FIG. 14B shows another example of a merge sharing region (1410) definedbased on a size threshold of 64 pixels. The merge sharing region (1410)includes three sub-blocks (1411)-(1413) having sizes of 32, 64, and 32pixels, respectively. The merge sharing region (1410) has a size of 128pixels that is larger than the size threshold, and includes twosub-blocks (1411) and (1413) that have a size smaller than the sizethreshold.

In other examples, determination of a merge sharing region can be basedon a different definition. For example, an ancestor node of leaf CUshaving a block size smaller than a threshold can be determined to be amerge sharing region. Using FIG. 14B as an example, when a threshold of64 pixels is used, either of the blocks 1411-1413 can be determined tobe a merge sharing region.

In addition, in some examples, no samples of the merge sharing node areoutside the picture boundary. During a parsing stage, if an ancestornode satisfies a definition of a merge sharing region, but has somesamples outside a picture boundary, this ancestor node will not betreated as a merge sharing node. Child CUs within this node may next beevaluated to determine a merge sharing region.

The shared merge candidate list algorithm can support translationalmerge/skip modes, such as regular merge mode, CRP mode (or IBC mode),triangle partition mode, sbTMVP mode, MMVD mode, and the like. In someexamples, affine merge mode is excluded for encoding blocks in a mergesharing region. Those merge/skip modes can be combined with an HMVPtable when being used within a merge sharing region. For thosemerge/skip modes, the behavior of shared merge candidate list algorithmis similar to that based on a regular merge candidate list. The sharedmerge candidate list algorithm just generates candidates for a mergesharing node pretending the merge sharing node is a leaf CU.

It is noted that leaf CUs within a merge sharing region may be codedusing coding modes other than a merge/skip mode. For example, a CUwithin a merge sharing node may be coded with an intra mode, or an intermode other than the merge/skip mode (e.g., AMVP mode).

IV. HMVP Table Updating for CUs within a Merge Sharing Region

In some examples, the merge sharing region scheme is employed to enableparallel processing of sub-blocks within a merge sharing region. Inaddition, the merge sharing region scheme can be combined with the HMVPscheme to improve inter picture coding performance. For example, when amerge sharing region is identified at a parsing stage at a decoder, ashared merge list can be constructed for the merge sharing region. Theconstruction of the merge sharing region can include HMVP candidatesfrom an HMVP table. Sub-blocks (or coding blocks) within the mergesharing region can be coded with an intra prediction mode (intra mode),or an inter prediction mode (inter mode). For each inter codedsub-block, corresponding motion information can be used to update theHMVP table.

However, according to an aspect of the disclosure, performing HMVP tableupdating for each inter coded sub-block (or coding block) within themerge sharing region may be unnecessary. For example, the sub-blockswithin the merge sharing region are close to each other. There is a highprobability that the neighboring inter coded blocks have similar motioninformation. In addition, those sub-blocks within the merge sharingregion share the same merge list. There is a high probability thatdifferent inter coded sub-blocks would use a same merge candidate astheir motion information as a result of a merge mode decoding process.Thus, HAVP table updating based on that similar motion information wouldbe redundant. In contrast, performing HMVP table updating for a subsetof those inter-coded blocks may be more suitable and can savecomputational cost associated with HMVP table updating.

Accordingly, in some embodiments, restrictions are applied to the HMVPtable updating process when the merge sharing region method and the HMVPmethod are combined. For example, instead of performing an HMVP tableupdating whenever an inter coded sub-block is decoded, only a subset ofthe inter coded sub-blocks within a merge sharing region will incur anHMVP table updating operation. In this way, cost of HMVP table updatingcan be avoided or reduced, and coding quality can be maintained.

In an embodiment, no HMVP table updating is performed for inter codedsub-blocks within a merge sharing region.

In some embodiments, whether an inter coded sub-block within a mergesharing region incurs HMVP table updating depends on what type of interprediction mode is used for encoding/decoding the correspondingsub-block.

FIG. 15 shows a table (1500) of inter prediction modes (inter modes)that can be used within a merge sharing region. Motion information canbe generated when one of those inter modes is used for encoding/decodinga sub-block within a merge sharing region. The motion information mightbe used for updating an HMVP table. The inter modes in the table (1500)can be separated into two categories: merge/skip mode and AMVP mode.

In AMVP mode, an AMVP candidate list can be constructed for encoding asub-block. The AMVP candidate list can include a set of AMVP candidatesselected from neighboring blocks of the sub-block. An HMVP table may beemployed for constructing the AMVP mode in an example. Motion estimationcan be performed to determine motion information for the sub-block. Adifference between a selected AMVP candidate and the motion informationresulting from the motion estimation can be signaled from an encoder toa decoder together with an index to the selected AMVP candidate on theAMVP candidate list. When decoding the sub-block at the decoder, theoriginal motion information is recovered based on the signaleddifference and the index. In some examples, the AMVP candidate list isseparately constructed from a shared merge list corresponding to thesub-block. In some examples, the AMVP candidate list can be a subset ofthe corresponding shared merge list. In some examples, the correspondingshared merge list can be used as the AMVP candidate list.

The merge/skip mode in the table (1500) can include two groups of codingmodes: Group I and Group II. Group I includes inter modes that use amerge candidate on a shared merge list as motion information forencoding or decoding a sub-block (leaf CU) within a merge sharingregion. Examples of inter modes in Group I can include regular mergemode, CRP mode, and the like. When a Group I inter mode is used forencoding a sub-block within a merge sharing region, a candidate on ashared merge list can be selected to provide motion information fordetermine a prediction for the sub-block. Subsequently, a difference(residue) between the prediction and the sub-block can be coded andtransmitted. When skip mode is employed, no residue signal is generatedor transmitted.

Group II includes inter modes that use motion information determinedbased on a merge candidate on a share merge list for encoding ordecoding a sub-block within a merge sharing region. Examples of intermodes in Group II can include triangle partition mode, sbTMVP mode, MMVDmode, and the like. When a Group II inter mode is used for encoding asub-block within a merge sharing region with a shared merge list, motioninformation can be constructed based on merge candidates on the sharedmerge list (e.g., triangle partition mode). Or, a merge candidate on theshared merge list can be used to determine a target block and motioninformation of sub-blocks within the target block can be obtained forencoding the sub-block within the merge sharing region (e.g., sbTMVPmode). Or, a merge candidate on the shared merge list can be used toprovide an initial point on a reference picture to facilitate a searchfor motion information over positions neighboring the initial point(e.g., MMVD). In the above cases, the resulting motion information canbe different from the merge candidates on the shared merge list.

Based on the categorization of the table (1500), in an embodiment, whena sub-block within a merge sharing region is inter coded with amerge/skip mode, no HMVP table updating is performed after the sub-blockis decoded. In contrast, when a sub-block within a merge sharing regionis inter coded with a coding mode other than a merge/skip mode, such asan AMVP mode, motion information resulting from decoding the sub-blockis used to update an HMVP table.

As described, a merge/skip mode, when used for encoding or decoding asub-block within a merge sharing region, is based on a shared mergelist. The shared merge list may include motion information that isalready included in an HMVP table recently. Motion information resultingfrom the merge/skip mode can be the same as or similar to a mergecandidate on the shared merge list, and thus may have a high probabilityof being already included in the HMVP table. Accordingly, updating theHMVP table with that information may be inefficient.

In contrast, in an AMVP mode, a motion difference is determined andencoded. Accordingly, motion information resulting from the AMVP modecan be different from an AMVP candidate on an AMVP candidate list (whichmay be similar to or different from a share merge list). Thus, themotion information has a low probability of being already included inthe HMVP table. Updating the HMVP table with the motion information canbe beneficial.

In another embodiment, when a sub-block within a merge sharing region isinter coded with a Group I mode (e.g., regular merge mode, or CRP mode),no HMVP table updating is performed with motion information of thesub-block. In contrast, when a sub-block within a merge sharing regionis inter coded with an inter mode other than a Group I mode, such as aGroup II mode, or an AMVP mode, motion information resulting fromdecoding the sub-block is used to update an HMVP table.

As described, a Group II inter mode, when used for encoding or decodinga sub-block within a merge sharing region, determines motion informationof the sub-block based on a merge candidate on a share merge list, butthe determined motion information can be different from the mergecandidate on the share merge list, and have a certain probability of notbeing included in an HVMP table. Thus, updating an HMVP table withmotion information resulting from a Group II mode may achieve somecoding gain in certain scenarios.

In some embodiments, one sub-block is selected from a set of inter codedsub-blocks within a merge sharing region for updating an HMVP table. Forexample, there are a plurality of inter coded sub-blocks, for example,coded with the inter prediction modes in the table (1500) according toan encoding/decoding order (e.g., a raster scan order, a zig-zag order,or the like). The first or a last sub-block according to the codingorder can be selected to update the HMVP table. For the other intercoded sub-blocks, no HMVP table updating is performed. In this way, anHMVP table updating cost can be reduced.

In various embodiments, for inter coded blocks not included a mergesharing region, HMVP table updating can be performed with correspondingmotion information of those inter coded blocks.

FIG. 16 shows a flow chart outlining a process (1600) according to anembodiment of the disclosure. The process (1600) can be used fordecoding a merge sharing region based on an HMVP table. In variousembodiments, the process (1600) are executed by processing circuitry,such as the processing circuitry in the terminal devices (210), (220),(230) and (240), the processing circuitry that performs functions of thevideo decoder (310), the processing circuitry that performs functions ofthe video decoder (410), and the like. In some embodiments, the process(1600) is implemented in software instructions, thus when the processingcircuitry executes the software instructions, the processing circuitryperforms the process (1600). The process starts at (S1601) and proceedsto (S1610).

At (S1610), a merge sharing region including a plurality of codingblocks is received. For example, a decoder can receives a bitstream ofcoding blocks partitioned from a picture. At a parsing stage, the mergesharing region can be determined based on a size threshold.

At (S1620), a shared merge candidate list can be constructed fordecoding the merge sharing region. HMVP candidates from an HMVP tablecan be added to the shared merge candidate list. The share mergecandidate list can include other types of merge candidates such asspatial merge candidates, temporal merge candidates, pair-wise averagebi-prediction candidates, or the like.

At (S1630), the merge sharing region can be decoded based on the sharemerge candidate list. For example, the coding blocks within the mergesharing region can be inter coded or intra coded. For the inter codedblocks, motion information can be determined during the decodingprocess. However, in order to reduce HMVP table updating cost, not allthe inter coded blocks will incur an HMVP updating operation.

In an example, no HMVP updating operation is performed for coding blockswithin the merge sharing region. In an example, whether to update theHMVP table with motion information of a coding block in the mergesharing region can depends on the type of the inter prediction mode usedfor coding the respective coding block. In an example, one coding block(e.g., a first or last one according to a coding order) can be selectedfrom the inter coded blocks within the merge sharing region, motioninformation of which can be used to update the HMVP table. The process(1600) can proceed to (S1699), and terminate at (S1699).

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 17 shows a computersystem (1700) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 17 for computer system (1700) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1700).

Computer system (1700) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1701), mouse (1702), trackpad (1703), touchscreen (1710), data-glove (not shown), joystick (1705), microphone(1706), scanner (1707), camera (1708).

Computer system (1700) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1710), data-glove (not shown), or joystick (1705), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1709), headphones(not depicted)), visual output devices (such as screens (1710) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1700) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1720) with CD/DVD or the like media (1721), thumb-drive (1722),removable hard drive or solid state drive (1723), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1700) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1749) (such as, for example USB ports of thecomputer system (1700)); others are commonly integrated into the core ofthe computer system (1700) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1700) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1740) of thecomputer system (1700).

The core (1740) can include one or more Central Processing Units (CPU)(1741), Graphics Processing Units (GPU) (1742), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1743), hardware accelerators for certain tasks (1744), and so forth.These devices, along with Read-only memory (ROM) (1745), Random-accessmemory (1746), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1747), may be connectedthrough a system bus (1748). In some computer systems, the system bus(1748) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1748),or through a peripheral bus (1749). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1741), GPUs (1742), FPGAs (1743), and accelerators (1744) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1745) or RAM (1746). Transitional data can be also be stored in RAM(1746), whereas permanent data can be stored for example, in theinternal mass storage (1747). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1741), GPU (1742), massstorage (1747), ROM (1745), RAM (1746), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1700), and specifically the core (1740) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1740) that are of non-transitorynature, such as core-internal mass storage (1747) or ROM (1745). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1740). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1740) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1746) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1744)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

Appendix A: Acronyms

ASIC: Application-Specific Integrated Circuit

BMS: benchmark set

CANBus: Controller Area Network Bus

CD: Compact Disc

CPUs: Central Processing Units

CRT: Cathode Ray Tube

CTBs: Coding Tree Blocks

CTUs: Coding Tree Units

CU: Coding Unit

DVD: Digital Video Disc

FPGA: Field Programmable Gate Areas

GOPs: Groups of Pictures

GPUs: Graphics Processing Units

GSM: Global System for Mobile communications

HEVC: High Efficiency Video Coding

HRD: Hypothetical Reference Decoder

IC: Integrated Circuit

JEM: joint exploration model

LAN: Local Area Network

LCD: Liquid-Crystal Display

LTE: Long-Term Evolution

MV: Motion Vector

OLED: Organic Light-Emitting Diode

PBs: Prediction Blocks

PCI: Peripheral Component Interconnect

PLD: Programmable Logic Device

PUs: Prediction Units

RAM: Random Access Memory

ROM: Read-Only Memory

SEI: Supplementary Enhancement Information

SNR: Signal Noise Ratio

SSD: solid-state drive

TUs: Transform Units,

USB: Universal Serial Bus

VUI: Video Usability Information

VVC: versatile video coding

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video decoding at a video decoder,comprising: receiving a merge sharing region including a plurality ofcoding blocks; constructing a shared merge candidate list for the mergesharing region; and decoding the merge sharing region based on theshared merge candidate list, wherein at least one inter coded codingblock within the merge sharing region is processed without updating ahistory-based motion vector prediction (HMVP) table with motioninformation of the at least one inter coded coding block, and motioninformation of a last inter coded coding block within the merge sharingregion according to a decoding order is used to update the HMVP table,and other inter coded coding block(s) within the merge sharing region isprocessed without updating the HMVP table with motion information of theother inter coded coding block(s).
 2. The method of claim 1, wherein allinter coded blocks in the merge sharing region are processed withoutupdating the HMVP table with motion information of any of the intercoded blocks.
 3. The method of claim 1, wherein the coding block(s)within the merge sharing region that is inter coded with a merge mode ora skip mode is processed without updating the HMVP table with motioninformation of the coding block(s).
 4. The method of claim 1, whereinthe coding block(s) within the merge sharing region that is inter coded(i) using a merge candidate on the shared merge candidate list as motioninformation of the coding block(s), or (ii) using motion informationdetermined based on a merge candidate on the shared merge candidate listis processed without updating the HMVP table with motion information ofthe coding block(s).
 5. The method of claim 1, wherein the codingblock(s) within the merge sharing region that is coded based on theshared merge candidate list is processed without updating the HMVP tablewith motion information of the coding block(s).
 6. The method of claim1, wherein the coding block(s) within the merge sharing region that isinter coded using a merge candidate on the shared merge candidate listas motion information of the coding block(s) is processed withoutupdating the HMVP table with motion information of the coding block(s).7. The method of claim 1, wherein motion information of a first intercoded coding block within the merge sharing region according to adecoding order is used to update the HMVP table, and the other intercoded coding block(s) within the merge sharing region is processedwithout updating the HMVP table with the motion information of the otherinter coded coding block(s).
 8. An apparatus of video decoding,comprising circuitry configured to: receive a merge sharing regionincluding a plurality of coding blocks; construct a shared mergecandidate list for the merge sharing region; and decode the mergesharing region based on the shared merge candidate list, wherein atleast one inter coded coding block within the merge sharing region isprocessed without updating a history-based motion vector prediction(HMVP) table with motion information of the at least one inter codedcoding block, and motion information of a last inter coded coding blockwithin the merge sharing region according to a decoding order is used toupdate the HMVP table, and other inter coded coding block(s) within themerge sharing region is processed without updating the HMVP table withmotion information of the other inter coded coding block(s).
 9. Theapparatus of claim 8, wherein all inter coded blocks in the mergesharing region are processed without updating the HMVP table with motioninformation of any of the inter coded blocks.
 10. The apparatus of claim8, wherein the coding block(s) within the merge sharing region that isinter coded with a merge mode or a skip mode is processed withoutupdating the HMVP table with motion information of the coding block(s).11. The apparatus of claim 8, wherein the coding block(s) within themerge sharing region that is inter coded (i) using a merge candidate onthe shared merge candidate list as motion information of the codingblock(s), or (ii) using motion information determined based on a mergecandidate on the shared merge candidate list is processed withoutupdating the HMVP table with motion information of the coding block(s).12. The apparatus of claim 8, wherein the coding block(s) within themerge sharing region that is coded based on the shared merge candidatelist is processed without updating the HMVP table with motioninformation of the coding block(s).
 13. The apparatus of claim 8,wherein the coding block(s) within the merge sharing region that isinter coded using a merge candidate on the shared merge candidate listas motion information of the coding block(s) is processed withoutupdating the HMVP table with motion information of the coding block(s).14. The apparatus of claim 8, wherein motion information of a firstinter coded coding block within the merge sharing region according to adecoding order is used to update the HMVP table, and the other intercoded coding block(s) within the merge sharing region is processedwithout updating the HMVP table with the motion information of the otherinter coded coding block(s).
 15. A non-transitory computer-readablemedium storing instructions executable by a processor to perform amethod of video decoding, the method comprising: receiving a mergesharing region including a plurality of coding blocks; constructing ashared merge candidate list for the merge sharing region; and decodingthe merge sharing region based on the shared merge candidate list,wherein at least one inter coded coding block within the merge sharingregion is processed without updating a history-based motion vectorprediction (HMVP) table with motion information of the at least oneinter coded coding block, and motion information of a last inter codedcoding block within the merge sharing region according to a decodingorder is used to update the HMVP table, and other inter coded codingblock(s) within the merge sharing region is processed without updatingthe HMVP table with motion information of the other inter coded codingblock(s).
 16. The non-transitory computer-readable medium of claim 15,wherein the coding block(s) within the merge sharing region that isinter coded with a merge mode or a skip mode is processed withoutupdating the HMVP table with motion information of the coding block(s).17. The non-transitory computer-readable medium of claim 15, wherein thecoding block(s) within the merge sharing region that is inter codedusing a merge candidate on the shared merge candidate list as motioninformation of the coding block(s) is processed without updating theHMVP table with motion information of the coding block(s).
 18. Thenon-transitory computer-readable medium of claim 15, wherein motioninformation of a first inter coded coding block within the merge sharingregion according to a decoding order is used to update the HMVP table,and the other inter coded coding block(s) within the merge sharingregion is processed without updating the HMVP table with the motioninformation of the other inter coded coding block(s).